Bruce Arena said this week that the LA Galaxy have “been the best team in the league since July.”

It was no empty boast. On Sunday night at The Home Depot Center, LA’s players backed up their manager’s words with a comprehensive 3-0 rout of the Seattle Sounders that put the Galaxy on the threshold of a second consecutive MLS Cup final.

Robbie Keane scored twice and playoff savant Mike Magee added his third of the postseason as LA played with far more energy and creativity than the visitors. On one fewer day of rest and hit by a couple of key injuries, the Sounders simply couldn’t keep up and now must win the return leg of the Western Conference finals—scheduled for Nov. 18—by at least three goals to force overtime.

The Galaxy, who had an awful start to the season, have lost just three times since Independence Day and on Sunday looked every bit a championship favorite.

Seattle shuffle

Sounders coach Sigi Schmid gambled a bit on Sunday and went with a conservative lineup that, theoretically, might hold off LA in the opener and put Seattle in prime position for the second game.

“We’ve got to bunker in and get used to playing a defensive part at times, but also get after them when we have our chances,” defender Jeff Parke said this week.

Playmaker Mauro Rosales (hamstring) was absent for the second straight match and striker Eddie Johnson (hamstring) was held out until the 65th minute. With left back Marc Burch suspended and Leo Gonzalez (hamstring) unavailable, Schmid deployed Zach Scott on defense and Alex Caskey in left midfield. Osvaldo Alonso and Brad Evans would hold down the middle while Christian Tiffert played behind snake-bit forward Fredy Montero, who would go scoreless for a ninth consecutive playoff game over four seasons.

Seattle (16-9-12) held a good bit of possession during the first half but never really threatened LA goalkeeper Josh Saunders. There were signs of trouble in the 14th minute, however, as Landon Donovan raced down the right wing and was hauled down by Jhon Kennedy Hurtado. The Sounders’ left flank was vulnerable and the Galaxy (19-13-6) would exploit it ruthlessly.

In the 28th, Keane and Donovan presented a preview of horrors to come on a slick give-and-go that resulted in a sharp header from the U.S. national team icon that was saved by Seattle’s Michael Gspurning. David Beckham, lined up in the middle, was drifting right to whip in crosses.

The Sounders were about to break.

“Just patience, really,” Keane told ESPN when asked how LA managed to carve open a team that hadn’t yielded a playoff goal in 315 minutes. “With the players we have, just continue to keep plugging away and keep playing the way we’ve been playing, (we knew) that we’d always open up teams.”

Galaxy’s brightest stars

Defender Sean Franklin got it started in first-half stoppage time, finding space on Seattle’s left wing and hitting a pass that midfielder Christian Wilhelmsson touched deftly to Donovan. With speed and precision, Donovan tore toward the endline and twisted his body to hit a floating cross back toward the left post, where Keane was waiting for the open header. It was the Irishman’s third goal of the playoffs, 19th of the season and 16th since he returned from European Championship duty in late June.

It was the third assist in four postseason matches for the rejuvenated Donovan, who has a goal as well.

“Robbie is the beneficiary of a couple of things. One, we’re playing a lot better and two, he’s getting in great spots and when he’s getting chances, he’s burying them,” Donovan told reporters this week. “He makes our job really easy, he always wants the ball, he puts himself in dangerous spots and if we do our job and get him the ball then he’s going to score more often than not.”

LA nearly doubled the lead in the 57th when Donovan’s cross, intended for Wilhelmsson, was cleared by Caskey. But the onslaught didn’t stop. In the 64th, Keane and Franklin (again, down Seattle’s left) combined to set the table for Magee.

This being the playoffs, the 28-year-old midfielder made no mistake and finished cleanly. Since his arrival to LA in 2009, Magee has 13 goals in 95 regular-season games and eight in 15 playoff games.

“There are certain players this time of year that play at a different level and Mike is one of them,” Donovan said. “Technically, Mike and Robbie are our two best finishers and our two best strikers of the ball, so when (Magee) gets a chance, he’s lethal.”

It was 3-0 just three minutes later. Donovan put Seattle’s defense into disarray once again with a run and shot that was deflected toward Wilhelmsson. The Swede was stymied by Gspurning, but Keane was there to clean up the rebound from close range.

The Sounders were fortunate it wasn’t worse. LA’s pace and fluid movement continued to cause problems and nearly resulted in a fourth goal on several occasions.

Looking ahead

The one major blip on LA’s run of form came in early August, when the Sounders inflicted a stunning 4-0 defeat at CenturyLink Field.

The host’s opening goal that day was set up by Rosales and scored by Johnson. That critical pair now has a week to heal up and they must be close to 100 percent if Seattle has any hope to overturn the deficit. Only once in MLS history has the opening game of a two-leg series been decided by three goals, and the Sounders were the victims then as well. After falling behind, 3-0, to Real Salt Lake last year, Seattle won the second game 2-0 and was eliminated.

Donovan left Sunday’s match in the 82nd minute with cramps but will have time to rest up before next Sunday’s match in Seattle. Other than that, the Galaxy are relatively healthy (defender A.J. DeLaGarza is out long term with a knee injury) and will appreciate a week’s rest following a string of five games in 15 days.

If the advantages in both conference finals hold, an MLS Cup rematch is in the offing. While LA looks to maintain its margin, the Houston Dynamo will head to DC United with a 3-1 lead of its own. If both advance, it would mean a second consecutive Galaxy-Dynamo showdown in Carson, Calif., where a Galaxy team that has found its groove would be the favorite once again.